While creating and evolving my program and knowledge, i came to get stuck again by the common brain errors of my self, writing something without sense for a machine. So I have to go again and starte to resolve my error by trying to spot that place where my brain failed in the code, or my code failed in the brain... . Maybe 2 complete days passed trying to find that spot-that error, passing again and again throug all my code, doing another complete simpler program solely to spot the problem, and finally spotting it i came to this very rare simple thing. In a vertex shader method, this:
PS VS( VS input )
{
PS output = (PS)0;
output.Pos = input.Pos; //----> position=float4(5.0f,5.0f,5.0f,5.0f) or whatever value
output.Tex = input.Tex;
return output;
}

I think it has to do with the fact that to represent a point or vector in 3d space, you need 3 coordinates, and to transform those coordinates using rotations, etc you multiply it against an appropriate matrix. A 3x1 Vector multiplied by a 3x3 Matrix will give you another 3x1 vector, representing the transformed point.

The issue is that a 3x3 Matrix can represent rotation and scaling, but can't include translation. To do that we need to use a 4x4 matrix. But in order for that to work, our original 3x1 point needs to be expanded to 4x1, since you can't multiply a 3x1 vector by a 4x4 matrix. The new coordinate, w, controls if the translation part of the 4x4 matrix is added to the result, so under most circumstances you want it to have a value of 1.0. However, if you're transforming a vector instead of a point, you don't want the translation applied, since a vector is an offset from 0,0,0 and the translation will change the vector's direction and magnitude, so you can use the same transformation matrix as before, but set the w coordinate of the vector to be 0.

I think that ordinarily, Direct3D takes care of adding that w=1.0f term automatically when it expands from a float3 to a float4, so when you use input.Pos, the value would be correct.

That is correct. The 0 W is meant to cancel out any translations a 4×X matrix would do on a 1×4 matrix (a vector) (or an X×4 and 4×1).
And when implicitly adding a 4th component to a vector it is set to 1. All other implicitly added components are set to 0.